Hypergolicity or self-ignition is a very desirable characteristic for biliquid propellants to have because this characteristic would eliminate the need for a separate ignition system to initiate the combustion of the propellant. The biliquid hypergolic propellant is comprised of an oxidizer and fuel which self ignites when brought together in a device such as a rocket engine combustion chamber. Mere hypergolic ignitability is, however, not adequate for successful performance since the ignition delay needs to be sufficiently short so that the rocket engine does not undergo a "hard start". The hypergolic ignitability characteristic must be capable of bringing about smooth combustion, and have "multiple start and restart" capabilities. For acceptable hypergolicity, an ignition delay of less than 50 milliseconds is considered essential.
Biliquid propellant fuels have been generally grouped into the following classes (1) liquid hydrogen and light elements, (2) borohydrides, (3) organic fuels, and (4) nitrogen hydrides. Examples of light elements are lithium, beryllium, boron, and aluminum. Examples of borohydrides are diborane (B.sub.2 H.sub.6) and pentaborane (B.sub.5 H.sub.9). Liquid organic fuels are all liquid fuels containing carbon and hydrogen. Examples of liquid organic fuels are alcohols, light hydrocarbon, unsymmetrical dimethylhydrazine (UDMH), and diethylenetriamine (DETA). Examples of nitrogen hydrides are ammonia (NH.sub.3) and hydrazine (N.sub.2 H.sub.4).
The mere fact a fuel is hypergolic with a certain oxidizer does not establish a preferred status for its use as a biliquid hypergolic propellant. As indicated by the above classes of available biliquid fuels a wider selection is available for use; however, the atoms most useful as an oxidizer for use in a biliquid propellant system are oxygen and fluorine. Certain compounds containing oxygen and/or fluorine are also useful as oxidizers. For example: chlorine trifluoride, nitrogen trifluoride, red fuming nitric acid, inhibited red fuming nitric acid, and hydrogen peroxide are oxidizing compounds of the described type. More recently more complex compounds have been synthesized.
Advantageous would be an oxidizer which could be rendered more useful for use with conventional fuels or whose oxidizer function could be improved so that the oxidizer could then be useful with other materials which normally have not been considered fuel candidates. For example, natural products or mixture thereof which are endemic in a particular country could then become useful fuels and provide low-cost liquid propellant compositions when used with the oxidizer when modified.
An object of this invention is to provide a method of imparting hypergolicity to non-hypergolic rocket propellants.
Another object of this invention is to provide a modified oxidizer which has the capacity to impart hypergolicity to a fuel-oxidizer combination which otherwise is non-hypergolic.
A further object of this invention is to provide biliquid hypergolic propellants which have an ignition delay of less than 50 milliseconds.
Still a further object of this invention is to provide a modified oxidizer for use in combination with fuels to yield repeatability of ignition times and to enable variations of modified oxidizer-to-fuel ratios to be selected wherein only a marginal effect to ignition times result.